Conventional bonded flexible pipe is described in American Petroleum Institute document API Specification 17J. These types of pipe are typically used for both “sweet” and “sour” service production, including export and injection services. Fluids transported include oil, gas, water and injection chemicals and gas. A typical construction is made up of a plurality of tubular layers, starting with an interlocking metal carcass and followed by a liner tube of plastic to retain the fluid within the pipe. Hoop strength armor reinforcement in the hoop direction is provided by helical metal wires which may be in several layers and wound in opposite helical directions. Additional layers may also be used, with a final jacket extrusion to complete the assembly, with a tough wear-resistant material.
1. Composite Pipe
U.S. Pat. Nos. 5,261,462 and 5,435,867, both issued to Donald H. Wolfe et al., are examples of tubular composite pipe in the prior art. Those patents relate to tubular structures having a plastic (i.e., polymeric) tube for the fluid conductor, which has an outer layer formed from alternating spirally wound strips of composite and elastomer. It is believed that the prior art composite pipes, such as disclosed in the above patents, have been limited to relatively short commercial lengths, by reason of the method by which such tubular structures have been made.
Typically, composite flexible pipes are made by filament winding, which involves turning the pipe while feeding and moving resin impregnated fibers from bobbins back and forth along the length of the pipe. Such technique limits the length of the reinforced flexible pipe which can be manufactured because of the number of bobbins required for the large number of fibers that are used in each pass. As a practical matter, it was not known how to make relatively long lengths of composite pipe sufficient for subsea use because of such problem.
In single bobbin machines, unloading and reloading time is a function of the time taken to thread each end of the fibers, the number of bobbins, and the time required to replace each bobbin. Also, due to the material payload requirements, a single bobbin-type machine will require each end to travel some distance from its bobbin over rollers, sheaves, eyelets, etc., through the machine to the closing point on the pipe, thus creating a time-consuming task. Because of the hundreds, and even thousands of bobbins, extremely large machines would be required to make a composite-reinforced pipe in long lengths using such prior art techniques. Consequently, the industry has not had available composite flexible pipes in long lengths suitable for subsea production and well operations. Multiple fiber tows are also not practical for long pipe lengths because of the fiber loading times required.
2. Long Flexible Composite Pipe
As described in U.S. Pat. Nos. 6,491,779, 6,804,942, and 7,073,978, all issued to Michael J. Bryant, discrete tapes are first formed from fibers and resin or the like, so that the tapes are wound on spools, which reduces the number of bobbins required as compared to the number of bobbins required for single fiber filaments, whereby it is possible to manufacture long lengths of composite flexible pipe. The tapes are initially formed and then are fed from tape spools rather than the fiber bobbins in the prior art. Also, each tape is composed of a plurality of superimposed thin tape strips formed of predominantly, unidirectional fibers, which are impregnated with an epoxy or other suitable bonding resin which cures with heat, cold, ultraviolet (UV) or other curing methods. The multi-layer tapes are wrapped with a polyethylene or similar plastic or thin metallic strip or covered by thermoplastic extrusion to confine them as a unit together, with bonding adhesive between the tape strips being prevented from escaping from the wrap. Each tape thus made is fed from a tape spool to the tubular core as the tubular core is rotated, or as the spools are rotated relative to the core, which produces helical wraps of each of the tapes on the tubular core in the same or opposite helical directions for reinforcement of the core.
FIGS. 1-5 illustrate prior art flexible composite tubing that forms a basis for the improvement provided by the present invention. Consequently, elements identified in FIGS. 1-5 correspondingly have reference relevance in FIGS. 6 and 7 illustrating embodiments of the present invention.
Referring now to FIG. 1, a preassembled fiber tape strip is shown which is formed of a plurality of fibers 11 which extend parallel to each other in the warp direction which is the main direction of the tape. Those fibers are made of fiber glass, Kevlar, carbon or similar materials. Fibers 12 are disposed perpendicular to the fibers 11 and extend underneath them and typically are joined together with a stitch in the manufacturing and assembly process. Such fibers 12 are in the weft direction across the tape strip. Preferably, the majority strength of the tape strip is provided in the direction of the fibers 11, and in some instances each strip of tape may be formed solely of warp fibers 11. Also, strips of thin metal of steel, aluminum, or other metal, some being perforated, may be used between or outside of the fiber strips in each laminate 15.
The fiber matrix formed of the fibers 11 and 12 may be separately formed and thereafter impregnated with a resin such as an epoxy resin, or the fiber matrix may be made on the same machine that impregnates such fibers with the resin.
FIG. 2 is an illustration of the tape strip T of the prior art invention (and by extension this invention), one form of which is made by impregnating the fibers 11 and with an epoxy resin or the like to form a single laminate 15. The laminates need to be as thin as possible to reduce strain in them when they are bent onto a pipe surface. Typically, the thickness of each laminate layer is from about 0.010″ to about 0.030″. This is somewhat of a trade-off between (a) very thin tape which provides for very efficient but long production process, and (b) a thicker tape which is less efficient (more strain) but requires less production time.
Each laminate 15 which is formed by the prior art and this invention is a separate tape T. A plurality of such tapes T are superimposed on each other as shown in FIG. 3 and, as will be explained, are bonded together by an adhesive which may initially be an uncured epoxy or resin between the tapes T which is later cured during or after the tapes A are wrapped on the core C. Once the adhesive between the tapes cures, the overall laminate product A assumes the radius to which it was bent. This happens because the tapes 15 slide over each other, and then when the adhesive cures, they cannot slide.
In FIG. 3, the finished tape A is shown in cross-section schematically with the warp fibers 11 exposed at the ends, and the epoxy impregnating and bonding the multiple tapes into the final tape T. The weft fibers are not shown in FIG. 3 because they extend across FIG. 3 just behind the cut line for FIG. 3.
An external protective jacket 20 of nylon, polyethylene, or similar flexible thermoplastic or elastomeric material surrounds the superimposed tapes T and encloses the adhesive between such tapes T so that none of the uncured adhesive escapes from the jacket 20 during curing.
A typical arrangement for forming the final tape A shown in FIG. 3 is illustrated by the equipment schematically shown in FIG. 4.
By way of example, the laminates 15 or tapes T are arranged in a superimposed relationship and are fed through squeeze rollers 25. Prior to reaching the squeeze rollers 25, the tapes T are spaced apart so that adhesive in the form of a resin or the like is applied between the tapes T with any suitable type of applicator 27 or spray which supplies adhesive or resin from an injector 28 and header 29 suitably connected to the applicator 27.
Guide rollers 35 serve to maintain the tapes T in a superimposed alignment with each other.
Finally, a rotatable spool 37 which has a wrapping sheet 39 of polyethylene, nylon or similar flexible thermoplastic or elastomeric material thereon is positioned for feeding a helical wrap of the sheet 39 to form a protective jacket 20 by rotating the spool head 37. Such protective jacket 20 is thus formed by the sheet 39 being wrapped about the tapes T to form the final multitape product A shown in cross-section in FIG. 3. Instead of the helical wraps of sheet 39, a “cigarette” wrap may be formed by a longitudinal sheet that extends lengthwise of the tape T, and which is folded to partially or fully extend around or substantially around the tape T. The helical sheet 39 preferably may then be wrapped outside of the cigarette wrap to complete product A.
Referring now to FIG. 5, a simple pipe construction is illustrated for showing the use of the tape A for reinforcing an inner core or tube C which is formed of a flexible fluid conducting material such as flexible polyethylene or metal which is thick enough to have some rigidity but thin enough to still be flexible without significant deformation or collapse. An anti-abrasive (flexible sheet or membrane) layer B of relatively thin polyethylene or the like is preferably disposed between the helical wraps of the tapes A to provide for anti-abrasion between two layers of the helical wraps. Although the wraps of the tapes A are shown as opposite helical wraps, the invention is not limited thereto. For example, the construction may have two or more wraps with a left hand lay, and two or more with a right hand lay, and then two or more with a left hand lay.
It is noted that the tapes A are in a non-bonding relationship to the core or tube C and to each other so that when the core or tube C flexes during use, the tapes A may slide to a limited extent relative to the core or tube C and to each other to permit the flexing of the entire assembly. Additionally, it is noted that there are small gaps or helical spaces 40 between each of the tapes A to provide for limited relative movement of the tapes A with respect to the core or tube C and to each other for flexibility when the core or tube C is flexed.
3. Insulating Tubing
Producing oil and gas in deep water or in extreme climates can make insulating pipe important in flow assurance. The common method of using steel pipe in such insulating pipe designs creates very heavy, expensive and difficult to install pipe that requires significant engineering and equipment to manufacture and install. None of the flexible composite tubing described above is inherently insulating in character.
Notwithstanding the above-described advances in flexible tubing provided by the inventions described in U.S. Pat. Nos. 6,491,779, 6,804,942, and 7,073,978, a method for insulating such tubing, while at the same time retaining its lightweight characteristics, would be very beneficial.